hi mujeeb
no, there is not such mechanism.
adding a naive locking is not hard... and it's probably good enough for most use cases. (of course one will need to handle the case when a document is closed in a abruptly (system or application crash, network disconnection).
this having been said, there is one more important drawback, which is a bit harder to solve: scribus tends to write full paths to images in the .sla file and if the resources are not exactly at the same place (mount point of the server / home) on each computer you will not be able to correctly share the document. (moving to a different computer is one of the reasons for using "collect for output")
both of those features need a bit of planning but can be implemented by people who are not yet into the scribus code.